The “space holder” method is a well-known process for making metallic foam structures and employs dissolvable or otherwise removable space-holding materials that are combined with metallic powders and subsequently removed from the combination by various methods, including heat or liquid dissolution, leaving behind a porous matrix formed from the metallic powder. The porous matrix material is then sintered to further strengthen the matrix structure. Numerous variations on the space holder concept are known in the art. See, e.g., U.S. Pat. Nos. 3,852,045; 6,849,230; U.S. Pub. Nos. 2005/0249625; 2006/0002810.
Surface roughness is an important attribute of orthopedic implants that are intended for cementless fixation to bone. High surface roughness can correspond to elevated friction against bone and general stability upon initial implantation, both of which are conducive to long-term stability via bone and tissue ingrowth. Several porous coating products have been developed for use in connection with implant surfaces, including implant coatings that are said to enhance biological fixation and maximize tissue ingrowth. Such coatings are applied to the face of an implant in order to impart a rough, high friction surface that interacts with bone in a manner that leads to a decrease in relative movement between the implant and the bone while providing a network of interconnected pores for secure fixation of the implant to bone by the ingrowth of bone tissue.